[ASan] Fix stack-overflow test for PowerPC

[foad]

Summary

Tweak the asan stack overflow heuristics to cope with PowerPC64 redzones,
which are larger than on x86-64: 288 bytes for big-endian and 512 bytes
for little-endian.

[samsonov]

Looks reasonable to me. Evgeniy, any objections?

[eugenis]

Perfect.
Writing tests finally pays off :)

lib/asan/asan_posix.cc

void AsanOnSIGSEGV(int, void *siginfo, void *context) {
   uptr addr = (uptr)((siginfo_t*)siginfo)->si_addr;
   int code = (int)((siginfo_t*)siginfo)->si_code;
   // Write the first message using the bullet-proof write.
   if (13 != internal_write(2, "ASAN:SIGSEGV\n", 13)) Die();
   uptr pc, sp, bp;
   GetPcSpBp(context, &pc, &sp, &bp);
 
   // Access at a reasonable offset above SP, or slightly below it (to account
-  // for x86_64 redzone, ARM push of multiple registers, etc) is probably a
-  // stack overflow.
+  // for x86_64 or PowerPC redzone, ARM push of multiple registers, etc) is
+  // probably a stack overflow.
   // We also check si_code to filter out SEGV caused by something else other
   // then hitting the guard page or unmapped memory, like, for example,
   // unaligned memory access.
-  if (addr + 128 > sp && addr < sp + 0xFFFF &&
+  if (addr + 512 > sp && addr < sp + 0xFFFF &&
       (code == si_SEGV_MAPERR || code == si_SEGV_ACCERR))
     ReportStackOverflow(pc, sp, bp, context, addr);
   else
     ReportSIGSEGV("SEGV", pc, sp, bp, context, addr);
 }
 
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